(1) Field of the Invention
The invention relates to an inflatable packing device including a sophisticated elastomeric cover means.
(2) Definitoio of Terms
As used herein and in the claims, the phrase "inflation initiation" refers to the location or point on the exterior of the device where first flexing of the contour of the device resulting from effective inflation is expected to occur. Inflation initiation can occur at a plurality of locations or points, depending upon choice of design.
As used herein and in the claims, the phrase "inflation element" means: the sub-assembly generally composed of the bladder, ribs, cover, upper securing means and lower collars or securing means.
As used herein and in the claims, the phrase "point of contact" means: the initial and subsequently latest expected location of interface between the exterior of the device and the wall of the well during effective inflation.
As used herein and in the claims, the phrase "effective inflation" means: the quantum of expansion of the bladder during the setting of the packing device from the run-in position of the apparatus to from between no more than about 70% to no more than about 85%, by volume, of the interior of the bladder when fully set in the well bore.
As used herein and in the claims, the phrase "departure angle" means: the angle between a straight line parallel to the longitudinal axis of the well and along the inside diameter wall of the well passing through a point of contact and a straight line drawn tangent to the exterior surface of the device for an interval of length extending from the point of contact to a distance of about one run-in diameter, this line too passing through the same point of contact. The longitudinal axis of the borehole and the two lines defining the departure angle must all be coplanar.
As used herein and in the claims, the phrase "expansion profiles" means: the transitional forms taken by the flexible portion of the inflation element during effective inflation.
As used herein, the phrase "uniform inflation profiles" means: the circumstance when the "expansion profiles" taken by the inflation element closely approximate straight line profiles from the point of contact to the end of the collar.
As used herein, the phrase "expansion ratio" means: the ratio of the diameter of the fully set inflation element, divided by the run-in diameter of the inflation element.
(3) Description of the Prior Art
Inflatable packers, bridge plugs, and the like, have long been utilized in subterranean wells. Such inflatable tools normally comprise an inflatable elastomeric bladder element concentrically disposed around a central body portion, such as a tube or mandrel. A sheath of reinforcing slats or ribs is typically provided exteriorally around the bladder with an elastomeric packing cover concentrically disposed around at least a portion of the sheath. Generally, a medial portion of the sheath will be exposed and without a cover for providing anchoring engagement of the packer to the wall of the well. Pressured fluid is communicated from the top of the well or interior of the well bore by means of a down hole pump to the interior of the body and thence through radial passages provided for such purpose or otherwise around the exterior of the body to the interior of the bladder during inflation.
Normally, an upper securing means engages the upper end of the inflatable elastomeric bladder and the reinforcing sheath (if included in the design), sealably securing the upper end of the bladder relative to the body, while a lower collar or securing means engages the lower end of the bladder and reinforcing sheath, securing the lower end of the bladder for slidable and sealable movement relative to the exterior of the body, in response to inflation forces. The elastomeric cover may be secured to the exterior of the sheath or placed around the exterior of the bladder, in known fashion.
With inflatable packers of this type, it has been observed that the portion of the bladder adjacent the exposed sheath section of the packer prematurely inflates prior to the other portions of the bladder which are reinforced against expansion by the reinforcing sheath and/or the elastomeric packing cover element. When the inflation element expands, one end of the bladder moves toward the other end of the device, and the bladder area adjacent the exposed sheath inflates until it meets the wall of the well bore, which may be cased or uncased. If the well bore is uncased, the well bore will have an earthen wall, and if the well bore is cased, the wall of the well bore will be the internal diameter surface of the casing.
It has been noted in a number of prior art designs that when service conditions encompass moderate expansion ratios, a propensity for the bladder to pinch around the exterior of the body arises, creating either a seal or a convoluted fold in the bladder that sometimes prevents the effective communication of further fluid throughout the bladder and preventing contiguous inflation propagation. The pinching seal and/or fold(s) can become entrenched in the bladder whereupon they obstruct further passage of fluid employed for inflating the bladder and therein keep fluid from reaching the farthest portions of bladder to be inflated. When this occurs in service, it always results in a soft set condition and in the imminent loss of seal between the cover and wellbore. This problem is discussed in detail in Eslinger, et al. "Design and Testing of a High-Performance Inflatable Packer," SPE 37483, Society of Petroleum Engineers (1997).
Folds in the bladder can be expected to occur in prior art devices like that shown in FIG. 18 when the expansion ratio is greater than 2:1. Designs of this sort inherently experience large departure angles and unfavorable expansion profiles when the expansion ratio is about 2:1 or more. By utilization of the design of the present invention, the departure angle is preferably controlled at no more than about 15.degree. and the inflation element experiences a uniform inflation profile and therefore, no folds or pinches will occur even if the expansion ratio is 3:1, or even higher. Elimination of the propensity to form folds and pinches in the present invention can be attributed to exceptionally low departure angles throughout inflation and the propagation of uniform inflation profiles throughout effective inflation.
The formation of folds creates unusually high triaxial stresses and strains in the vicinity of the fold. Correspondingly, these triaxial stresses and strains create a condition that causes localized failure of the bladder by means of cracking and/or tearing. Failure occurs because the physical properties of the elastomeric material composing the bladder are not adequate to survive the localized triaxial stresses and strains. Except for the devices described in my patents U.S. Pat. No. 5,469,919, U.S. Pat. No. 5,564,504 and U.S. Pat. No. 5,813,459, all other prior art devices having an element construction similar to that shown in FIG. 18 experience large departure angles and unfavorable expansion profiles when the expansion ratio is greater that 2.00:1, i.e., departure angles greater than 25.degree. at a 2:1 expansion ratio and expansion profiles similar to that shown in FIG. 18. An expansion profile would be deemed unfavorable if the slope of the exterior surface at any point on the inflation element exceeds 15.degree. relative to the longitudinal axis of the wellbore. The term "unfavorable expansion profile" is only applicable to the "effective inflation" portion of the inflation cycle. The propensity to form pinching seals and folds is directly related to undesirable combinations of expansion ratio, departure angles and expansion profiles of the device. In prior art devices, pinching seals and folds are experienced upon the combination of departure angles greater than about 15.degree. and an expansion ratio greater than about 2.25:1.
With regard to covers, at expansion ratios of 2:1 and more, the departure angle in prior art devices other than those for the preferred embodiments in my aforementioned patents will be greater than 20.degree. and the combination of a departure angle greater than 20.degree. and an expansion ratio greater than about 2:1 has been observed to result in cracking and tearing in covers. Once a tear or tears occur, non-uniform rib spacing results. Non-uniform load distribution within the cover also occurs and general discontinuity of the cover results. These conditions, in turn, can result in extrusion of the bladder between ribs resulting in subsequent failure of the bladder and service failure of the device.
In my U.S. Pat. Nos. 5,469,919, 5,564,504, and 5,813,459 entitled "Programmed Shaped Inflatable Packer Device," issued Sep. 29, 1998, I disclose methods to abate the formation of pinching seals and folds during inflation of prior art devices by using a design which includes a series of shaped-controlling means on an elastomeric packing cover along the length of the bladder in the form of high and low modulus modules of varying lengths and thicknesses. While this design is an advancement in the art, the design of the modules leaves comparatively sharp angled transitional chamfers and significant size differences between the high and low modules. These chamfers and different diameters are of such magnitude that they are easily detected by the naked eye. The short transitional chamfers give rise to localized stresses and strains in expanded covers. These localized stresses and strains can cause cracking and/or tearing in the covers which can ultimately result in device failure.
In another prior art device which was subjected to service conditions having expansion ratios of 2.35:1 and 3:1, the minimum achievable departure angles were about 15.degree. and 23.degree., respectively. This device used a plateau cover interval concept in accordance with my patents U.S. Pat. No. 5,469,919, U.S. Pat. No. 5,564,504 and U.S. Pat. No. 5,813,459 and has been made commercially available by High Pressure Integrity, Inc. under the product name "Z-44". While this product was an advancement and improvement over other prior art devices, the variations of constant thickness cover intervals with abrupt and relatively short transitions from one thickness to another caused comparatively high localized stress and strain concentrators in the cover which occasionally resulted in cracking and tearing of the cover. Z-44 and similar devices always exhibited rib kinking and experienced occasional rib cutting of the bladder. Additionally, inflation profiles exhibited plateau intervals (intervals of constant diameter along the length of the device) rather than relatively straight sloped profiles in the interval between the last point of contact with the casing (POC) and the end of the collar. Additionally, the plateau cover interval concept abated the formation of pinches and folds in bladders at moderate expansion ratios, but did not eliminate their occurrence at expansion ratios greater than 2.35:1.
The ability to successfully deflate and retrieve an inflatable device is a common service requirement. A pinch or fold might still have formed in a bladder during inflation even though the inflation element effected a satisfactory seal against the wall of the well. During deflation, a fold can pinch and seal around the body, obstructing the transmission of fluid out of the lower portions of the bladder and thereby prevent complete deflation of the bladder. Once a fold is formed, it is permanently entrenched in bladder and results in multiple layers of bladder beneath the ribs. These layers in turn result in a deflated diameter which is greater than the initial run-in diameter of the inflation element. Retrieval of the device to the earth's surface is thus compromised since the device might not be able to pass through restrictions in the well bore as it is moved upwardly therein.
I have now discovered that the problems described above can be further abated by providing an inflatable packing device having a combination of an excellent uniform expansion profile during effective inflation and minimal departure angles throughout the inflation cycle. This combination results in contiguous propagation of expansion profiles that are not achievable in any prior art devices.
The invention permits orchestration of varying sophisticated contours and configurations in the cover means to provide a uniform expansion profile in an expected, i.e., pre-determinable, manner which can be achieved with only minimal or nominal experimentation which will be within the ordinary skills of those knowledgeable in the design and use of inflatable elastomeric devices for use in subterranean wells, and by adhering to the teachings herein.